New bioreactor produces green gas with early stage microorganisms

A new type of biological plant in Ibbenbüren has now fed the first green methane into the natural gas network. Raw materials are water, green electricity and carbon dioxide, which comes from a biogas plant. Instead of a chemical conversion process that takes place under high pressure and relatively high temperatures, the developers at the Friedrich-Alexander-Universität Erlangen-Nürnberg and the Ostbayerischen Technische Hochschule Regensburg rely on the oldest living creatures in the world, archaea, also known as primeval animals. They only need a few nutrients to convert the raw materials. Particularly high pressure is also not necessary, and at 60 degrees Celsius the process temperature is moderate. This means that the energy consumption is low. In addition, the microorganisms are tolerant of contamination. Only oxygen has to be reliably kept out.

Industrie ist mit von der Partie

Biologische Methanisierungsanlagen betreiben bereits das Martinsrieder Unternehmen Electrochaea und MicrobEnergy in Schwandorf. Mit dem Bioreaktor, in dem die Umwandlung von Wasserstoff und Kohlendioxid in Methan stattfindet, sind sie allerdings nicht sonderlich zufrieden. Hier kommen die Forscher aus Bayern ins Spiel, an ihrer Spitze Professor Michael Sterner, der in Regensburg lehrt. Mit seinem Team hat er, begleitet von den beiden Unternehmen, die für eine Nutzung in Frage kommen, im Rahmen des Projekts Orbit einen so genannten Rieselbettreaktor entwickelt, der eine um 20 Prozent höhere Effektivität hat als der bisher genutzte Rührreaktor, schätzt Sterner.

Industry is involved

The Martinsried company Electrochaea and MicrobEnergy already operate biological methanation plants in Schwandorf. However, they are not particularly satisfied with the bioreactor, in which hydrogen and carbon dioxide are converted into methane. This is where the researchers from Bavaria come into play, at their head Professor Michael Sterner, who teaches in Regensburg. Together with his team, accompanied by the two companies that are eligible for use, as part of the Orbit project, he has developed what is known as a trickle bed reactor, which is 20 percent more effective than the previously used stirred reactor, says Sterner.

Intimate contact with the archaea

In a trickle reactor, hydrogen and carbon dioxide are injected from below. The liquid in which the archaea are located trickles from above. The freshly generated methane escapes upwards and is so pure that it can be fed into the grid straight away. The process ensures intimate contact between the gases and the microorganisms and thus a better conversion of the starting gases into methane.

Electricity for gaps in green generation

With the phasing out of nuclear energy and coal-fired power, the need to provide energy for lulls, nights and days with little sunshine increases when wind and solar power weaken. Building batteries on a large scale is too expensive. That is why many scientists and electricity suppliers prefer power-to-gas technology. With green electricity, water is split into water and oxygen. Hydrogen and carbon dioxide can be converted into methane, which is fed into the grid. If there is a lack of electricity, it can be used to generate electricity. There are, however, two problems: Germany cannot produce enough green electricity by far. And a lot of energy is lost in the double conversion.